An axial turbomachine, for example a gas turbine, has a turbine in which hot gas is expanded. For achieving high thermal efficiency of the gas turbine, the temperature of the hot gas at the inlet into the turbine is to be selected as high as possible. The maximum achievable temperature level of the hot gas is limited by strength requirements of the turbine which are defined by construction and material selection of the components of the turbine. The temperature load and the mechanical stress of the components define their service life which for reasons of reliability and economy has to lie above specified limits.
A conventional turbine rotor has a shaft and disks which are rotationally symmetrically attached thereupon, on the outer edge of which disks are fastened a multiplicity of rotor blades which lie next to each other over the circumference. The rotor blades and the disks are sometimes the most severely stressed components in the turbine, as a result of which maintenance cycles of the gas turbine are defined principally by these components. For extending the running times of the rotor blades and of the disks, it is known to cool the rotor blades and the disks with cooling air which is conventionally tapped from a compressor of the gas turbine. The rotor blades are especially produced from an intricate structure which is traversed by cooling passages through which flows the cooling air for cooling the rotor blades. The cooling passages open into the rotor blade root at which the cooling passages are fed with the cooling air.
Conventionally, such as in the case of the design according to US 2005/0265849 A1, provision is made on the disk in the region of the blade root for a cooling air inflow passage which is formed between the disk and an annular sealing plate which is adjacent thereto and is directly adjacently arranged radially on the blade root. Design demands are made on the one-piece, platform-like sealing plate to the effect of minimizing leakage of cooling air as far as possible and of preventing entry of hot gas into the cooling passages. For this reason, the sealing plate, on its radially outer edge, is provided with a sealing ring which, by centrifugal force, comes to bear against the undersides of the platforms of the blades.
Instead of a sealing ring, a seal-point may also be provided. However, on account of different thermal expansions of the components and also on account of the relative position of the sealing plate and of the blade root to each other resulting therefrom during operation of the axial turbomachine rotor, wear of the seal-points ensues. As a result, the sealing effect of the seal-points is degraded so that at the sealing plate cooling air can flow into the hot gas region of the turbine. Furthermore, there is the risk of hot gas, bypassing the seal-points, being able to penetrate into the cooling passages and consequently increase the thermal loading of the rotor blades, as a result of which the risk of a premature failure of the rotor blades is increased.
In addition, an end-face sealing of the cooling air inflow passage, in which instead of a one-piece, annular sealing plate provision is made for a multiplicity of sealing plate segments which jointly form the sealing ring, is known from WO 2007/028703 A1. By centrifugal force, these bear against the undersides of the platforms of the rotor blades. A separate seal by means of a sealing ring is therefore not necessary.